<?php

/**
 * @file
 * Parse iCal data.
 *
 * This file must be included when these functions are needed.
 */

/**
 * Return an array of iCalendar information from an iCalendar file.
 *
 *   No timezone adjustment is performed in the import since the timezone
 *   conversion needed will vary depending on whether the value is being
 *   imported into the database (when it needs to be converted to UTC), is being
 *   viewed on a site that has user-configurable timezones (when it needs to be
 *   converted to the user's timezone), if it needs to be converted to the
 *   site timezone, or if it is a date without a timezone which should not have
 *   any timezone conversion applied.
 *
 *   Properties that have dates and times are converted to sub-arrays like:
 *      'datetime'   => date in YYYY-MM-DD HH:MM format, not timezone adjusted
 *      'all_day'    => whether this is an all-day event
 *      'tz'         => the timezone of the date, could be blank for absolute
 *                      times that should get no timezone conversion.
 *
 *   Exception dates can have muliple values and are returned as arrays
 *   like the above for each exception date.
 *
 *   Most other properties are returned as PROPERTY => VALUE.
 *
 *   Each item in the VCALENDAR will return an array like:
 *   [0] => Array (
 *     [TYPE] => VEVENT
 *     [UID] => 104
 *     [SUMMARY] => An example event
 *     [URL] => http://example.com/node/1
 *     [DTSTART] => Array (
 *       [datetime] => 1997-09-07 09:00:00
 *       [all_day] => 0
 *       [tz] => US/Eastern
 *     )
 *     [DTEND] => Array (
 *       [datetime] => 1997-09-07 11:00:00
 *       [all_day] => 0
 *       [tz] => US/Eastern
 *     )
 *     [RRULE] => Array (
 *       [FREQ] => Array (
 *         [0] => MONTHLY
 *       )
 *       [BYDAY] => Array (
 *         [0] => 1SU
 *         [1] => -1SU
 *       )
 *     )
 *     [EXDATE] => Array (
 *       [0] = Array (
 *         [datetime] => 1997-09-21 09:00:00
 *         [all_day] => 0
 *         [tz] => US/Eastern
 *       )
 *       [1] = Array (
 *         [datetime] => 1997-10-05 09:00:00
 *         [all_day] => 0
 *         [tz] => US/Eastern
 *       )
 *     )
 *     [RDATE] => Array (
 *       [0] = Array (
 *         [datetime] => 1997-09-21 09:00:00
 *         [all_day] => 0
 *         [tz] => US/Eastern
 *       )
 *       [1] = Array (
 *         [datetime] => 1997-10-05 09:00:00
 *         [all_day] => 0
 *         [tz] => US/Eastern
 *       )
 *     )
 *   )
 *
 * @todo
 *   figure out how to handle this if subgroups are nested,
 *   like a VALARM nested inside a VEVENT.
 *
 * @param string $filename
 *   Location (local or remote) of a valid iCalendar file.
 *
 * @return array
 *   An array with all the elements from the ical.
 */
function date_ical_import($filename) {
    // Fetch the iCal data. If file is a URL, use drupal_http_request. fopen
    // isn't always configured to allow network connections.
    if (substr($filename, 0, 4) == 'http') {
        // Fetch the ical data from the specified network location.
        $icaldatafetch = drupal_http_request($filename);
        // Check the return result.
        if ($icaldatafetch->error) {
            watchdog('date ical', 'HTTP Request Error importing %filename: @error', array('%filename' => $filename, '@error' => $icaldatafetch->error));
            return FALSE;
        }
        // Break the return result into one array entry per lines.
        $icaldatafolded = explode("\n", $icaldatafetch->data);
    } else {
        $icaldatafolded = @file($filename, FILE_IGNORE_NEW_LINES);
        if ($icaldatafolded === FALSE) {
            watchdog('date ical', 'Failed to open file: %filename', array('%filename' => $filename));
            return FALSE;
        }
    }
    // Verify this is iCal data.
    if (trim($icaldatafolded[0]) != 'BEGIN:VCALENDAR') {
        watchdog('date ical', 'Invalid calendar file: %filename', array('%filename' => $filename));
        return FALSE;
    }
    return date_ical_parse($icaldatafolded);
}

/**
 * Returns an array of iCalendar information from an iCalendar file.
 *
 * As date_ical_import() but different param.
 *
 * @param array $icaldatafolded
 *   An array of lines from an ical feed.
 *
 * @return array
 *   An array with all the elements from the ical.
 */
function date_ical_parse($icaldatafolded = array()) {
    $items = array();

    // Verify this is iCal data.
    if (trim($icaldatafolded[0]) != 'BEGIN:VCALENDAR') {
        watchdog('date ical', 'Invalid calendar file.');
        return FALSE;
    }

    // "Unfold" wrapped lines.
    $icaldata = array();
    foreach ($icaldatafolded as $line) {
        $out = array();
        // See if this looks like the beginning of a new property or value. If not,
        // it is a continuation of the previous line. The regex is to ensure that
        // wrapped QUOTED-PRINTABLE data is kept intact.
        if (!preg_match('/([A-Z]+)[:;](.*)/', $line, $out)) {
            // Trim up to 1 leading space from wrapped line per iCalendar standard.
            $line = array_pop($icaldata) . (ltrim(substr($line, 0, 1)) . substr($line, 1));
        }
        $icaldata[] = $line;
    }
    unset($icaldatafolded);

    // Parse the iCal information.
    $parents = array();
    $subgroups = array();
    $vcal = '';
    foreach ($icaldata as $line) {
        $line = trim($line);
        $vcal .= $line . "\n";
        // Deal with begin/end tags separately.
        if (preg_match('/(BEGIN|END):V(\S+)/', $line, $matches)) {
            $closure = $matches[1];
            $type = 'V' . $matches[2];
            if ($closure == 'BEGIN') {
                array_push($parents, $type);
                array_push($subgroups, array());
            } elseif ($closure == 'END') {
                end($subgroups);
                $subgroup = &$subgroups[key($subgroups)];
                switch ($type) {
                    case 'VCALENDAR':
                        if (prev($subgroups) == FALSE) {
                            $items[] = array_pop($subgroups);
                        } else {
                            $parent[array_pop($parents)][] = array_pop($subgroups);
                        }
                        break;
                    // Add the timezones in with their index their TZID.
                    case 'VTIMEZONE':
                        $subgroup = end($subgroups);
                        $id = $subgroup['TZID'];
                        unset($subgroup['TZID']);

                        // Append this subgroup onto the one above it.
                        prev($subgroups);
                        $parent = &$subgroups[key($subgroups)];

                        $parent[$type][$id] = $subgroup;

                        array_pop($subgroups);
                        array_pop($parents);
                        break;
                    // Do some fun stuff with durations and all_day events and then append
                    // to parent.
                    case 'VEVENT':
                    case 'VALARM':
                    case 'VTODO':
                    case 'VJOURNAL':
                    case 'VVENUE':
                    case 'VFREEBUSY':
                    default:
                        // Can't be sure whether DTSTART is before or after DURATION, so
                        // parse DURATION at the end.
                        if (isset($subgroup['DURATION'])) {
                            date_ical_parse_duration($subgroup, 'DURATION');
                        }
                        // Add a top-level indication for the 'All day' condition. Leave it
                        // in the individual date components, too, so it is always available
                        // even when you are working with only a portion of the VEVENT
                        // array, like in Feed API parsers.
                        $subgroup['all_day'] = FALSE;

                        // iCal spec states 'The "DTEND" property for a "VEVENT" calendar
                        // component specifies the non-inclusive end of the event'. Adjust
                        // multi-day events to remove the extra day because the Date code
                        // assumes the end date is inclusive.
                        if (!empty($subgroup['DTEND']) && (!empty($subgroup['DTEND']['all_day']))) {
                            // Make the end date one day earlier.
                            $date = date_make_date($subgroup['DTEND']['datetime'] . ' 00:00:00', $subgroup['DTEND']['tz']);
                            date_modify($date, '-1 day');
                            $subgroup['DTEND']['datetime'] = date_format($date, 'Y-m-d');
                        }
                        // If a start datetime is defined AND there is no definition for
                        // the end datetime THEN make the end datetime equal the start
                        // datetime and if it is an all day event define the entire event
                        // as a single all day event.
                        if (!empty($subgroup['DTSTART']) &&
                                (empty($subgroup['DTEND']) && empty($subgroup['RRULE']) && empty($subgroup['RRULE']['COUNT']))) {
                            $subgroup['DTEND'] = $subgroup['DTSTART'];
                        }
                        // Add this element to the parent as an array under the component
                        // name.
                        if (!empty($subgroup['DTSTART']['all_day'])) {
                            $subgroup['all_day'] = TRUE;
                        }
                        // Add this element to the parent as an array under the
                        prev($subgroups);
                        $parent = &$subgroups[key($subgroups)];

                        $parent[$type][] = $subgroup;

                        array_pop($subgroups);
                        array_pop($parents);
                        break;
                }
            }
        }
        // Handle all other possibilities.
        else {
            // Grab current subgroup.
            end($subgroups);
            $subgroup = &$subgroups[key($subgroups)];

            // Split up the line into nice pieces for PROPERTYNAME,
            // PROPERTYATTRIBUTES, and PROPERTYVALUE.
            preg_match('/([^;:]+)(?:;([^:]*))?:(.+)/', $line, $matches);
            $name = !empty($matches[1]) ? strtoupper(trim($matches[1])) : '';
            $field = !empty($matches[2]) ? $matches[2] : '';
            $data = !empty($matches[3]) ? $matches[3] : '';
            $parse_result = '';
            switch ($name) {
                // Keep blank lines out of the results.
                case '':
                    break;

                // Lots of properties have date values that must be parsed out.
                case 'CREATED':
                case 'LAST-MODIFIED':
                case 'DTSTART':
                case 'DTEND':
                case 'DTSTAMP':
                case 'FREEBUSY':
                case 'DUE':
                case 'COMPLETED':
                    $parse_result = date_ical_parse_date($field, $data);
                    break;

                case 'EXDATE':
                case 'RDATE':
                    $parse_result = date_ical_parse_exceptions($field, $data);
                    break;

                case 'TRIGGER':
                    // A TRIGGER can either be a date or in the form -PT1H.
                    if (!empty($field)) {
                        $parse_result = date_ical_parse_date($field, $data);
                    } else {
                        $parse_result = array('DATA' => $data);
                    }
                    break;

                case 'DURATION':
                    // Can't be sure whether DTSTART is before or after DURATION in
                    // the VEVENT, so store the data and parse it at the end.
                    $parse_result = array('DATA' => $data);
                    break;

                case 'RRULE':
                case 'EXRULE':
                    $parse_result = date_ical_parse_rrule($field, $data);
                    break;

                case 'STATUS':
                case 'SUMMARY':
                case 'DESCRIPTION':
                    $parse_result = date_ical_parse_text($field, $data);
                    break;

                case 'LOCATION':
                    $parse_result = date_ical_parse_location($field, $data);
                    break;

                // For all other properties, just store the property and the value.
                // This can be expanded on in the future if other properties should
                // be given special treatment.
                default:
                    $parse_result = $data;
                    break;
            }

            // Store the result of our parsing.
            $subgroup[$name] = $parse_result;
        }
    }
    return $items;
}

/**
 * Parses a ical date element.
 *
 * Possible formats to parse include:
 *   PROPERTY:YYYYMMDD[T][HH][MM][SS][Z]
 *   PROPERTY;VALUE=DATE:YYYYMMDD[T][HH][MM][SS][Z]
 *   PROPERTY;VALUE=DATE-TIME:YYYYMMDD[T][HH][MM][SS][Z]
 *   PROPERTY;TZID=XXXXXXXX;VALUE=DATE:YYYYMMDD[T][HH][MM][SS]
 *   PROPERTY;TZID=XXXXXXXX:YYYYMMDD[T][HH][MM][SS]
 *
 *   The property and the colon before the date are removed in the import
 *   process above and we are left with $field and $data.
 *
 * @param string $field
 *   The text before the colon and the date, i.e.
 *   ';VALUE=DATE:', ';VALUE=DATE-TIME:', ';TZID='
 * @param string $data
 *   The date itself, after the colon, in the format YYYYMMDD[T][HH][MM][SS][Z]
 *   'Z', if supplied, means the date is in UTC.
 *
 * @return array
 *   $items array, consisting of:
 *      'datetime'   => date in YYYY-MM-DD HH:MM format, not timezone adjusted
 *      'all_day'    => whether this is an all-day event with no time
 *      'tz'         => the timezone of the date, could be blank if the ical
 *                      has no timezone; the ical specs say no timezone
 *                      conversion should be done if no timezone info is
 *                      supplied
 *  @todo
 *   Another option for dates is the format PROPERTY;VALUE=PERIOD:XXXX. The
 *   period may include a duration, or a date and a duration, or two dates, so
 *   would have to be split into parts and run through date_ical_parse_date()
 *   and date_ical_parse_duration(). This is not commonly used, so ignored for
 *   now. It will take more work to figure how to support that.
 */
function date_ical_parse_date($field, $data) {

    $items = array('datetime' => '', 'all_day' => '', 'tz' => '');
    if (empty($data)) {
        return $items;
    }
    // Make this a little more whitespace independent.
    $data = trim($data);

    // Turn the properties into a nice indexed array of
    // array(PROPERTYNAME => PROPERTYVALUE);
    $field_parts = preg_split('/[;:]/', $field);
    $properties = array();
    foreach ($field_parts as $part) {
        if (strpos($part, '=') !== FALSE) {
            $tmp = explode('=', $part);
            $properties[$tmp[0]] = $tmp[1];
        }
    }

    // Make this a little more whitespace independent.
    $data = trim($data);

    // Record if a time has been found.
    $has_time = FALSE;

    // If a format is specified, parse it according to that format.
    if (isset($properties['VALUE'])) {
        switch ($properties['VALUE']) {
            case 'DATE':
                preg_match(DATE_REGEX_ICAL_DATE, $data, $regs);
                // Date.
                $datetime = date_pad($regs[1]) . '-' . date_pad($regs[2]) . '-' . date_pad($regs[3]);
                break;
            case 'DATE-TIME':
                preg_match(DATE_REGEX_ICAL_DATETIME, $data, $regs);
                // Date.
                $datetime = date_pad($regs[1]) . '-' . date_pad($regs[2]) . '-' . date_pad($regs[3]);
                // Time.
                $datetime .= ' ' . date_pad($regs[4]) . ':' . date_pad($regs[5]) . ':' . date_pad($regs[6]);
                $has_time = TRUE;
                break;
        }
    }
    // If no format is specified, attempt a loose match.
    else {
        preg_match(DATE_REGEX_LOOSE, $data, $regs);
        if (!empty($regs) && count($regs) > 2) {
            // Date.
            $datetime = date_pad($regs[1]) . '-' . date_pad($regs[2]) . '-' . date_pad($regs[3]);
            if (isset($regs[4])) {
                $has_time = TRUE;
                // Time.
                $datetime .= ' ' . (!empty($regs[5]) ? date_pad($regs[5]) : '00') .
                        ':' . (!empty($regs[6]) ? date_pad($regs[6]) : '00') .
                        ':' . (!empty($regs[7]) ? date_pad($regs[7]) : '00');
            }
        }
    }

    // Use timezone if explicitly declared.
    if (isset($properties['TZID'])) {
        $tz = $properties['TZID'];
        // Fix alternatives like US-Eastern which should be US/Eastern.
        $tz = str_replace('-', '/', $tz);
        // Unset invalid timezone names.
        module_load_include('install', 'date_timezone');
        $tz = _date_timezone_replacement($tz);
        if (!date_timezone_is_valid($tz)) {
            $tz = '';
        }
    }
    // If declared as UTC with terminating 'Z', use that timezone.
    elseif (strpos($data, 'Z') !== FALSE) {
        $tz = 'UTC';
    }
    // Otherwise this date is floating.
    else {
        $tz = '';
    }

    $items['datetime'] = $datetime;
    $items['all_day'] = $has_time ? FALSE : TRUE;
    $items['tz'] = $tz;
    return $items;
}

/**
 * Parse an ical repeat rule.
 *
 * @return array
 *   Array in the form of PROPERTY => array(VALUES)
 *   PROPERTIES include FREQ, INTERVAL, COUNT, BYDAY, BYMONTH, BYYEAR, UNTIL
 */
function date_ical_parse_rrule($field, $data) {
    $data = preg_replace("/RRULE.*:/", '', $data);
    $items = array('DATA' => $data);
    $rrule = explode(';', $data);
    foreach ($rrule as $key => $value) {
        $param = explode('=', $value);
        // Must be some kind of invalid data.
        if (count($param) != 2) {
            continue;
        }
        if ($param[0] == 'UNTIL') {
            $values = date_ical_parse_date('', $param[1]);
        } else {
            $values = explode(',', $param[1]);
        }
        // Treat items differently if they have multiple or single values.
        if (in_array($param[0], array('FREQ', 'INTERVAL', 'COUNT', 'WKST'))) {
            $items[$param[0]] = $param[1];
        } else {
            $items[$param[0]] = $values;
        }
    }
    return $items;
}

/**
 * Parse exception dates (can be multiple values).
 *
 * @return array
 *   an array of date value arrays.
 */
function date_ical_parse_exceptions($field, $data) {
    $data = str_replace($field . ':', '', $data);
    $items = array('DATA' => $data);
    $ex_dates = explode(',', $data);
    foreach ($ex_dates as $ex_date) {
        $items[] = date_ical_parse_date('', $ex_date);
    }
    return $items;
}

/**
 * Parses the duration of the event.
 *
 * Example:
 *  DURATION:PT1H30M
 *  DURATION:P1Y2M
 *
 * @param array $subgroup
 *   Array of other values in the vevent so we can check for DTSTART.
 */
function date_ical_parse_duration(&$subgroup, $field = 'DURATION') {
    $items = $subgroup[$field];
    $data = $items['DATA'];
    preg_match('/^P(\d{1,4}[Y])?(\d{1,2}[M])?(\d{1,2}[W])?(\d{1,2}[D])?([T]{0,1})?(\d{1,2}[H])?(\d{1,2}[M])?(\d{1,2}[S])?/', $data, $duration);
    $items['year'] = isset($duration[1]) ? str_replace('Y', '', $duration[1]) : '';
    $items['month'] = isset($duration[2]) ? str_replace('M', '', $duration[2]) : '';
    $items['week'] = isset($duration[3]) ? str_replace('W', '', $duration[3]) : '';
    $items['day'] = isset($duration[4]) ? str_replace('D', '', $duration[4]) : '';
    $items['hour'] = isset($duration[6]) ? str_replace('H', '', $duration[6]) : '';
    $items['minute'] = isset($duration[7]) ? str_replace('M', '', $duration[7]) : '';
    $items['second'] = isset($duration[8]) ? str_replace('S', '', $duration[8]) : '';
    $start_date = array_key_exists('DTSTART', $subgroup) ? $subgroup['DTSTART']['datetime'] : date_format(date_now(), DATE_FORMAT_ISO);
    $timezone = array_key_exists('DTSTART', $subgroup) ? $subgroup['DTSTART']['tz'] : variable_get('date_default_timezone_name', NULL);
    if (empty($timezone)) {
        $timezone = 'UTC';
    }
    $date = date_make_date($start_date, $timezone);
    $date2 = drupal_clone($date);
    foreach ($items as $item => $count) {
        if ($count > 0) {
            date_modify($date2, '+' . $count . ' ' . $item);
        }
    }
    $format = isset($subgroup['DTSTART']['type']) && $subgroup['DTSTART']['type'] == 'DATE' ? 'Y-m-d' : 'Y-m-d H:i:s';
    $subgroup['DTEND'] = array(
        'datetime' => date_format($date2, DATE_FORMAT_DATETIME),
        'all_day' => isset($subgroup['DTSTART']['all_day']) ? $subgroup['DTSTART']['all_day'] : 0,
        'tz' => $timezone,
    );
    $duration = date_format($date2, 'U') - date_format($date, 'U');
    $subgroup['DURATION'] = array('DATA' => $data, 'DURATION' => $duration);
}

/**
 * Parse and clean up ical text elements.
 */
function date_ical_parse_text($field, $data) {
    if (strstr($field, 'QUOTED-PRINTABLE')) {
        $data = quoted_printable_decode($data);
    }
    // Strip line breaks within element.
    $data = str_replace(array("\r\n ", "\n ", "\r "), '', $data);
    // Put in line breaks where encoded.
    $data = str_replace(array("\\n", "\\N"), "\n", $data);
    // Remove other escaping.
    $data = stripslashes($data);
    return $data;
}

/**
 * Parse location elements.
 *
 * Catch situations like the upcoming.org feed that uses
 * LOCATION;VENUE-UID="http://upcoming.yahoo.com/venue/104/":111 First Street...
 * or more normal LOCATION;UID=123:111 First Street...
 * Upcoming feed would have been improperly broken on the ':' in http://
 * so we paste the $field and $data back together first.
 *
 * Use non-greedy check for ':' in case there are more of them in the address.
 */
function date_ical_parse_location($field, $data) {
    if (preg_match('/UID=[?"](.+)[?"][*?:](.+)/', $field . ':' . $data, $matches)) {
        $location = array();
        $location['UID'] = $matches[1];
        $location['DESCRIPTION'] = stripslashes($matches[2]);
        return $location;
    } else {
        // Remove other escaping.
        $location = stripslashes($data);
        return $location;
    }
}

/**
 * Return a date object for the ical date, adjusted to its local timezone.
 *
 * @param array $ical_date
 *   An array of ical date information created in the ical import.
 * @param string $to_tz
 *   The timezone to convert the date's value to.
 *
 * @return object
 *   A timezone-adjusted date object.
 */
function date_ical_date($ical_date, $to_tz = FALSE) {

    // If the ical date has no timezone, must assume it is stateless
    // so treat it as a local date.
    if (empty($ical_date['datetime'])) {
        return NULL;
    } elseif (empty($ical_date['tz'])) {
        $from_tz = date_default_timezone_name();
    } else {
        $from_tz = $ical_date['tz'];
    }
    if (strlen($ical_date['datetime']) < 11) {
        $ical_date['datetime'] .= ' 00:00:00';
    }
    $date = date_make_date($ical_date['datetime'], $from_tz);

    if ($to_tz && $ical_date['tz'] != '' && $to_tz != $ical_date['tz']) {
        date_timezone_set($date, timezone_open($to_tz));
    }
    return $date;
}

/**
 * Escape #text elements for safe iCal use.
 *
 * @param string $text
 *   Text to escape
 *
 * @return string
 *   Escaped text
 *
 */
function date_ical_escape_text($text) {
    $text = drupal_html_to_text($text);
    $text = trim($text);
    // TODO Per #38130 the iCal specs don't want : and " escaped
    // but there was some reason for adding this in. Need to watch
    // this and see if anything breaks.
    // $text = str_replace('"', '\"', $text);
    // $text = str_replace(":", "\:", $text);
    $text = preg_replace("/\\\b/", "\\\\", $text);
    $text = str_replace(",", "\,", $text);
    $text = str_replace(";", "\;", $text);
    $text = str_replace("\n", "\\n ", $text);
    return trim($text);
}

/**
 * Build an iCal RULE from $form_values.
 *
 * @param array $form_values
 *   An array constructed like the one created by date_ical_parse_rrule().
 *     [RRULE] => Array (
 *       [FREQ] => Array (
 *         [0] => MONTHLY
 *       )
 *       [BYDAY] => Array (
 *         [0] => 1SU
 *         [1] => -1SU
 *       )
 *       [UNTIL] => Array (
 *         [datetime] => 1997-21-31 09:00:00
 *         [all_day] => 0
 *         [tz] => US/Eastern
 *       )
 *     )
 *     [EXDATE] => Array (
 *       [0] = Array (
 *         [datetime] => 1997-09-21 09:00:00
 *         [all_day] => 0
 *         [tz] => US/Eastern
 *       )
 *       [1] = Array (
 *         [datetime] => 1997-10-05 09:00:00
 *         [all_day] => 0
 *         [tz] => US/Eastern
 *       )
 *     )
 *     [RDATE] => Array (
 *       [0] = Array (
 *         [datetime] => 1997-09-21 09:00:00
 *         [all_day] => 0
 *         [tz] => US/Eastern
 *       )
 *       [1] = Array (
 *         [datetime] => 1997-10-05 09:00:00
 *         [all_day] => 0
 *         [tz] => US/Eastern
 *       )
 *     )
 */
function date_api_ical_build_rrule($form_values) {
    $RRULE = '';
    if (empty($form_values) || !is_array($form_values)) {
        return $RRULE;
    }

    // Grab the RRULE data and put them into iCal RRULE format.
    $RRULE .= 'RRULE:FREQ=' . (!array_key_exists('FREQ', $form_values) ? 'DAILY' : $form_values['FREQ']);
    $RRULE .= ';INTERVAL=' . (!array_key_exists('INTERVAL', $form_values) ? 1 : $form_values['INTERVAL']);

    // Unset the empty 'All' values.
    if (array_key_exists('BYDAY', $form_values) && is_array($form_values['BYDAY'])) {
        unset($form_values['BYDAY']['']);
    }
    if (array_key_exists('BYMONTH', $form_values) && is_array($form_values['BYMONTH'])) {
        unset($form_values['BYMONTH']['']);
    }
    if (array_key_exists('BYMONTHDAY', $form_values) && is_array($form_values['BYMONTHDAY'])) {
        unset($form_values['BYMONTHDAY']['']);
    }

    if (array_key_exists('BYDAY', $form_values) && is_array($form_values['BYDAY']) && $BYDAY = implode(",", $form_values['BYDAY'])) {
        $RRULE .= ';BYDAY=' . $BYDAY;
    }
    if (array_key_exists('BYMONTH', $form_values) && is_array($form_values['BYMONTH']) && $BYMONTH = implode(",", $form_values['BYMONTH'])) {
        $RRULE .= ';BYMONTH=' . $BYMONTH;
    }
    if (array_key_exists('BYMONTHDAY', $form_values) && is_array($form_values['BYMONTHDAY']) && $BYMONTHDAY = implode(",", $form_values['BYMONTHDAY'])) {
        $RRULE .= ';BYMONTHDAY=' . $BYMONTHDAY;
    }
    // The UNTIL date is supposed to always be expressed in UTC.
    // The input date values may already have been converted to a date object on a
    // previous pass, so check for that.
    if (array_key_exists('UNTIL', $form_values) && array_key_exists('datetime', $form_values['UNTIL']) && !empty($form_values['UNTIL']['datetime'])) {
        // We only collect a date for UNTIL, but we need it to be inclusive, so
        // force it to a full datetime element at the last second of the day.
        if (!is_object($form_values['UNTIL']['datetime'])) {
            if (strlen($form_values['UNTIL']['datetime']) < 11) {
                $form_values['UNTIL']['datetime'] .= ' 23:59:59';
                $form_values['UNTIL']['granularity'] = serialize(drupal_map_assoc(array('year', 'month', 'day', 'hour', 'minute', 'second')));
                $form_values['UNTIL']['all_day'] = FALSE;
            }
            $until = date_ical_date($form_values['UNTIL'], 'UTC');
        } else {
            $until = $form_values['UNTIL']['datetime'];
        }
        $RRULE .= ';UNTIL=' . date_format($until, DATE_FORMAT_ICAL) . 'Z';
    }
    // Our form doesn't allow a value for COUNT, but it may be needed by
    // modules using the API, so add it to the rule.
    if (array_key_exists('COUNT', $form_values)) {
        $RRULE .= ';COUNT=' . $form_values['COUNT'];
    }

    // iCal rules presume the week starts on Monday unless otherwise specified,
    // so we'll specify it.
    if (array_key_exists('WKST', $form_values)) {
        $RRULE .= ';WKST=' . $form_values['WKST'];
    } else {
        $RRULE .= ';WKST=' . date_repeat_dow2day(variable_get('date_first_day', 0));
    }

    // Exceptions dates go last, on their own line.
    // The input date values may already have been converted to a date
    // object on a previous pass, so check for that.
    if (isset($form_values['EXDATE']) && is_array($form_values['EXDATE'])) {
        $ex_dates = array();
        foreach ($form_values['EXDATE'] as $value) {
            if (!empty($value['datetime'])) {
                $date = !is_object($value['datetime']) ? date_ical_date($value, 'UTC') : $value['datetime'];
                $ex_date = !empty($date) ? date_format($date, DATE_FORMAT_ICAL) . 'Z' : '';
                if (!empty($ex_date)) {
                    $ex_dates[] = $ex_date;
                }
            }
        }
        if (!empty($ex_dates)) {
            sort($ex_dates);
            $RRULE .= chr(13) . chr(10) . 'EXDATE:' . implode(',', $ex_dates);
        }
    } elseif (!empty($form_values['EXDATE'])) {
        $RRULE .= chr(13) . chr(10) . 'EXDATE:' . $form_values['EXDATE'];
    }

    // Exceptions dates go last, on their own line.
    if (isset($form_values['RDATE']) && is_array($form_values['RDATE'])) {
        $ex_dates = array();
        foreach ($form_values['RDATE'] as $value) {
            $date = !is_object($value['datetime']) ? date_ical_date($value, 'UTC') : $value['datetime'];
            $ex_date = !empty($date) ? date_format($date, DATE_FORMAT_ICAL) . 'Z' : '';
            if (!empty($ex_date)) {
                $ex_dates[] = $ex_date;
            }
        }
        if (!empty($ex_dates)) {
            sort($ex_dates);
            $RRULE .= chr(13) . chr(10) . 'RDATE:' . implode(',', $ex_dates);
        }
    } elseif (!empty($form_values['RDATE'])) {
        $RRULE .= chr(13) . chr(10) . 'RDATE:' . $form_values['RDATE'];
    }

    return $RRULE;
}
